Nobel Peace Prize winner Tawakul Karman of Yemen speaks to reporters at Sanaa International Airport upon her arrival from Egypt August 4, 2013. Egyptian airport authorities have barred Karman, a supporter of deposed president Mohamed Mursi, from entering the country, security sources said. (Khaled Abdullah/Reuters)

Authorities denied Yemeni Nobel laureate Tawakkol Karman entry into Egypt after she landed at the airport in Cairo on Sunday.

Karman, the first Arab woman to win the Nobel Peace Prize, has stated her opposition to the coup that ousted President Mohamed Morsi and had said she intended to join sit-ins by his supporters.

Airport officials said Karman was sent back on the Sunday flight that brought her to Cairo from the United Arab Emirates. They said her name had been placed by various security agencies on a stop list at the airport. The officials spoke on the condition of anonymity because they were not authorized to brief the media.

The decision to bar Karman suggests that authorities wanted to deny the pro-Morsi camp the publicity she would have generated, particularly the evidence that prominent figures outside Egypt oppose Morsi’s ouster. His supporters strongly condemned the action against Karman, saying it showed the “resurrection” of the Egyptian police state under autocrat Hosni Mubarak, toppled in a 2011 popular uprising.

Karman shared the 2011 Nobel Peace Prize with Liberia’s President Ellen Johnson Sirleaf and women’s rights campaigner Leymah Gbowee. She earned it for her role in the protests that swept Yemen that year and led to the departure from office of longtime ruler Ali Abdullah Saleh.

In Cairo, more than a month after the military overthrew Morsi, tens of thousands of the Islamist leader’s supporters remain camped at two main crossroads demanding his reinstatement. The military-backed interim leadership has warned that if they do not disperse, security forces will move in, setting the stage for a potential bloody showdown.

Also Sunday, authorities announced that the trial of the spiritual leader of the Muslim Brotherhood and his powerful deputy will start Aug. 25, the state news agency reported.

Mohammed Badie, leader of the Morsi-allied Brotherhood, and his deputy, Khairat el-Shater, are accused of complicity and incitement in the killing of eight demonstrators outside the group’s Cairo headquarters, the news agency said. Shater is in custody, but Badie is still at large.

Meanwhile, the United States and the European Union are trying to find a peaceful resolution to the standoff in Cairo. At least 140 pro-Morsi protesters have been killed in conflicts with security forces since the July 3 coup.

U.S. Deputy Secretary of State William J. Burns extended his visit to the capital by a day for further talks with Egyptian leaders. He met Sunday with Defense Minister Gen. Abdel Fatah al-Sissi, who led the coup. A member of the pro-Morsi delegation that met Saturday with Burns said there would be another round of talks with the U.S. diplomat.

Also in Cairo are the foreign ministers of the United Arab Emirates, which had been at sharp odds with Morsi’s government, and Qatar, which maintains close ties to the Brotherhood, as well as the European Union’s special envoy, Bernardino León.